The presence of discontinuities such as, for example, a weld, a weld heat-affected zone, a feature line, a feature bend, a mechanical fastener joint, a gauge change or a deep draw area that underwent mechanical deformation during manufacture, can negatively impact the structural performance of components and assemblies including, particularly, sheet metal components used in the production of motor vehicles. This is particularly true when those sheet metal components are made from work-hardened and/or heat-treated aluminum alloys.
More specifically, the strength and/or ductility of a weld and a weld heat-affected zone are almost always reduced below that of the parent substrate for aluminum alloys. In addition, the geometry of the welded joint may introduce a stress concentration that can lead to cracking under service conditions as well as during impact loading. Further, welds in aluminum alloys generally demonstrate lower load-bearing capability when exposed to peel loading rather than pure tensile shear.
Thin gauge, heat-treated 6XXX aluminum alloys such as those commonly used for automotive body panels are particularly susceptible to these issues. FIGS. 1a and 1b show such an aluminum roof panel R joined to a door opening panel D by a weld joint W. When subjected to a sufficient impact load from, for example, a vehicle accident, the aluminum roof panel R could buckle adjacent the weld W causing a load concentration at the weld operating in peel mode. See FIG. 1c. In extreme conditions this could result in the failure of the weld.
This document relates to (a) a method of enhancing in-service structural performance of a sheet metal component incorporating a discontinuity including, for example, a metal motor vehicle roof panel as well as to (b) such a roof panel heat-treated to overcome the potential problem.